CVD processing requires a number of vaporized processing liquids. These vaporized liquids are generated and supplied to a CVD chamber via a system of pipes (or "lines") and vaporizing mechanisms known as a gas delivery system. Typically a separate vaporizing mechanism is provided for vaporizing each processing liquid, and is coupled to a source of processing liquid and a source of carrier gas. Each vaporizing mechanism and processing liquid source combination within a gas delivery system is referred to as a vaporization stage. Although a number of vaporizing mechanisms exist (e.g., bubblers, injection valves, etc.), most conventional gas delivery systems employ a plurality of injection valves for vaporizing processing liquids to be delivered to a CVD chamber.
A typical injection valve comprises a processing liquid inlet for receiving a pressurized processing liquid, a carrier gas inlet for receiving a pressurized inert carrier gas, and an outlet for delivering a vaporized processing liquid/carrier gas mixture. The injection valve is heated such that when the processing liquid is injected into the carrier gas, the heat and the low partial vapor pressure of the processing liquid in the carrier gas causes the processing liquid to vaporize. A high carrier gas pressure produces more processing liquid vaporization by lowering the partial vapor pressure of the processing liquid within the carrier gas. Accordingly, when designing a gas delivery system, maintenance of adequate carrier gas pressure is an important consideration, as is minimizing overall system size and complexity.
To achieve a low partial vapor pressure for each processing liquid while minimizing system size, conventional gas delivery systems are configured such that a carrier gas is delivered (via a mass flow controller) to a first injection valve, where it is used to vaporize a first processing liquid, forming a first vaporized processing liquid/carrier gas mixture. The first vaporized processing liquid/carrier gas mixture then is delivered to the carrier gas inlet of a second, consecutive injection valve where it is used to vaporize a second processing liquid. A mixture of the first and second vaporized processing liquids and the carrier gas then is delivered to the carrier gas inlet of a third consecutive injection valve, etc. These configurations provide a compact and cost effective system as they employ a single gas line, and a single carrier gas source controlled by a single mass flow controller to achieve vaporization within each of the various vaporization stages. Additionally, conventional gas delivery systems facilitate processing liquid vaporization as the entire mass flow of carrier gas is applied to each injection valve.
Despite their overall compact and efficient design, maintenance of conventional gas delivery systems is expensive due to injection valve clogging. A clogged injection valve can cause downtime not only of the chamber to which the clogged injection valve is coupled, but also of upstream and/or downstream chambers. In addition to costly chamber downtime, injection valves themselves are expensive, typically costing more than two thousand dollars to replace, exclusive of labor costs. Thus, considerable effort has been devoted to developing clog resistant gas delivery systems, and numerous advances have been achieved.
A particularly worthy advance is the recognition by Applied Materials, Inc., that alloys containing nickel react with the CVD processing liquid TEPO, causing residue formation and clogging, and the recognition that chromium can repress the nickel/TEPO reaction. Thus, gas delivery components made with less than 1% nickel and with 16-27% chromium significantly reduce clogging as described in commonly assigned U.S. Pat. No. 5,925,189 (application Ser. No. 08/568,193, filed Dec. 6, 1995). Despite such advances, clogging within gas delivery systems remains a problem, particularly when a gas delivery system must be configured with existing nickel-containing components.
Accordingly, a need exists for a clog resistant gas delivery system that can be easily and inexpensively repaired, should clogging occur, and that resists clogging regardless of component composition.